1. Field of the Invention
The present invention relates to lasers and, more particularly, to lasers in which thermal energy charge transfer reactions take place.
2. Description of the Prior Art
The usefulness of lasers which operate at the visible and ultraviolet (UV) wavelengths, or ranges is well appreciated. Recently, a nitrogen ion laser pumped by charge transfer reaction, which operates in the visible range, has been described in the literature in the following listed references:
A. "Stimulated emission from charge-transfer reactions in the afterflow of an e-beam discharge into high-pressure helium-nitrogen mixtures" by C. B. Collins et al. Applied Physics Letters, Vol. 24, No. 10, May 15, 1974;
B. "A nitrogen ion laser pumped by charge transfer" by C. B. Collins et al. Applied Physics Letters Vol. 25. No. 6, Sept. 15, 1974.
C. "Scaling of the helium-nitrogen charge transfer laser" by Collins and Cunningham. Applied Physics Letters Vol. 27, No. 3, Aug. 1, 1975.
D. "Thermal modification of the kinetic sequence pumping the helium-nitrogen charge-transfer laser" by Collins et al. Applied Physics Letters Vol. 28. No. 9. May 1, 1976.
The laser described in the above listed references, hereinafter simply referred to as the Collins' laser, is one containing a mixture of helium and nitrogen. The laser is pumped by charge transfer from He.sub.2.sup.+ to N.sub.2.sup.+. When the stimulated emission takes place from B.sup.2 .SIGMA..sub.u.sup. + (v=0) state of the nitrogen ion (N.sub.2.sup.+) to its X.sup.2 .SIGMA..sub.g.sup.+ (v=1) state violet light at 427.8nm is produced. When the state transition is between the (0,2) or (0,3) vibrational components of B.sup.2 .SIGMA..sub.u.sup.+ and X.sup.2 .SIGMA..sub.g.sup.+, light at 470.9nm or at 522.8nm is produced.
In the Collins' laser the input or pumping energy is provided by a powerful electron beam (e-beam) which represents the major and most significant disadvantage of the laser. In one reported embodiment (reference c) of the Collins' laser, each pulse of the e-beam has a voltage on the order of 1Mv, at a current of 13Kamp and is of a duration of about 20nsec. Thus, the laser input power is about 260 joules (J). Clearly, the power necessary to produce such an e-beam pulse is much higher. The best reported output power under unspecified conditions is about 2.3Mw at 15-16 nsec or about 36mJ. Thus, the need for the e-beam in the collins' laser results in an extremely inefficient laser. More importantly, the machinery, e.g., the accelerometer, needed to produce the e-beam is very large, requiring a relatively large room to be accommodated in, is very complex and very expensive. Consequently, the laser is too cumbersome and expensive for many commercial as well as scientific applications.
Another disadvantage of the Collins' laser, which is a direct result of the need for the e-beam, is the fact that the laser can only operate at He pressure, which is believed to be considerably higher than the minimum needed for efficient charge transfer reaction to take place. As is appreciated He is practically transparent to an e-beam at relatively low pressure, e.g., several atmospheres. It is for this reason that in the latest publications concerning the Collins' laser, He pressure on the order of 34 atmospheres (atm) is suggested, even though in the earlier publications He pressures of 3 atm and 7 atm are reported. Consequently, the laser structure or chamber has to be designed to withstand such high He pressure.
A need therefore exists for a laser which operates on the charge transfer reaction principles to produce emission in the visible range, as is the case in the Collins' laser, but one in which other than an e-beam is used to activate the laser.